Improvements are continually being sought for seat belt pre-tensioner systems. One example of a pre-tensioner for a vehicular seat belt system is disclosed in U.S. Pat. No. 5,588,677 commonly owned by the Assignee of the present invention. The pre-tensioner includes a flexible draw element in the form of a wire cable, connected to the buckle part of a three-point seat belt system. The wire cable has a looped end secured to a roller in the buckle part. With one end of the loop portion secured against movement, a portion of the loop is pulled downwardly by a power operated device which includes a power operated piston attached to the cable. Typically, the power-operated device comprises a pyrotechnic gas generator that drives the piston a distance sufficient to remove slack from the seat belt system. The pulling force of the pre-tensioner on the buckle part is quite large, and is developed in a very short time. Operation of the power-operated device is typically triggered by an external sensor such as an acceleration sensor.
The system described above is but one of many pre-tensioner systems employing pyrotechnic gas generators. For example, the pretensioner can act on the buckle part, or instead can act directly on the belt webbing or the retractor in which it is wound. It is necessary in developing seat belt systems that various components and sub-systems be tested both individually and together to insure proper coordination in an emergency event where pre-tensioning is desired. In addition, the operation of components associated with the seat belt needs to be verified with different pretensioners. For instance, in typical three-point belt systems, the belt webbing is wound on a spool of a retractor that can include vehicle and/or web sensitive locking devices to stop belt payout from the retractor spool during emergency vehicle situations such as during high acceleration/deceleration conditions. The seat belt pathway can include an anchor along one side of the seat, a tongue and buckle connection at the other side of the side, and guide ring mounted generally at an elevated position in the vehicle passenger compartment such as to a B-pillar and/or to an adjustment mechanism for changing the position of the D-ring. When an emergency condition occurs, each of these components will generally experience higher stresses than during non-emergency conditions. It would be desirable to be able to identify how these components interact during high stress events.
In the course of developing a seat belt system, repetitive tests may be required with each test involving the firing of the pyrotechnic device. While it is desirable to avoid the complications associated with firing of pyrotechnic devices in a laboratory test condition, it is important that the testing accurately reflect the operating characteristics unique to the particular pyrotechnic devices in order to insure that the test conditions faithfully represent actual field-observable conditions of the seat belt system in operation.